6 research outputs found
Estimating flow heterogeneity in natural fracture systems
Examples of small to medium scale fault systems have been mapped in Jurassic sedimentary rocks in north Somerset, England. These examples include contractional and dilational strike-slip oversteps as well as normal faults. These maps form the basis of calculations performed to investigate heterogeneity in natural fracture systems with the aim of predicting fluid flow localisation in different fault styles. As there is no way to measure fracture aperture directly, we use vein thickness to represent an integrated flow path or ‘palaeo-aperture’ from which we derive a representation of the flow distribution. Three different methods are used to estimate flow heterogeneity based on: (1) fracture density (the ratio of fracture length to area), (2) fracture aperture (fracture porosity) and (3) hydraulic conductance (fracture permeability normalised to the pressure gradient and fluid properties).Our results show that fracture density and hydraulic conductance are poorly correlated and that fracture density does not fully represent the natural heterogeneity of fracture systems. Fracture aperture and hydraulic conductance indicate stronger degrees of flow localisation. Different types of structures also seem to display characteristic and predictable patterns of heterogeneity. Normal fault systems show the highest magnitude of localisation along the faults rather than in the relay ramps, while contractional and dilational strike-slip systems show very strong localisation in the faults and oversteps, respectively. In all cases the amount of damage in the oversteps can modify such patterns of heterogeneity. <br/
Study of fracture-induced anisotropy from discrete fracture network simulation of well test responses
Different conceptualizations of fracture networks have been generated in order to simulate well tests in fractured reservoirs. These models have two purposes: firstly to investigate whether the behaviour of realistic fracture networks can be emulated with more simple models; and secondly to assess whether different sources of anisotropy have characteristic and recognizable influences on the pressure derivative. The anisotropy of the fracture networks was increased by decreasing the angle between two originally orthogonal fracture sets, and by increasing the permeability contrast between two orthogonal fracture sets. Results indicate that simple models can capture the first-order behaviour of more realistic examples. However because early time data are strongly influenced by the connectivity of the fracture network, the degree of anisotropy can only be assessed at later times in a test. Increasing anisotropy results in increasing heterogeneity and compartmentalization, and permeability anisotropy in an orthogonal system can only partially replicate the behaviour of a geometrically anisotropic syste
Measurement of the Isolated Nuclear Two-Photon Decay in
International audienceThe nuclear two-photon or double-gamma () decay is a second-order electromagnetic process whereby a nucleus in an excited state emits two gamma rays simultaneously. To be able to directly measure the decay rate in the low-energy regime below the electron-positron pair-creation threshold, we combined the isochronous mode of a storage ring with Schottky resonant cavities. The newly developed technique can be applied to isomers with excitation energies down to keV and half-lives as short as ms. The half-life for the decay of the first-excited state in bare ions was determined to be ms, which strongly deviates from expectations
Measurement of the Isolated Nuclear Two-Photon Decay in
International audienceThe nuclear two-photon or double-gamma () decay is a second-order electromagnetic process whereby a nucleus in an excited state emits two gamma rays simultaneously. To be able to directly measure the decay rate in the low-energy regime below the electron-positron pair-creation threshold, we combined the isochronous mode of a storage ring with Schottky resonant cavities. The newly developed technique can be applied to isomers with excitation energies down to keV and half-lives as short as ms. The half-life for the decay of the first-excited state in bare ions was determined to be ms, which strongly deviates from expectations
Proton capture on stored radioactive Te ions
International audienceExperimental determination of the cross sections of proton capture on radioactive nuclei is extremely difficult. Therefore, it is of substantial interest for the understanding of the production of the p-nuclei. For the first time, a direct measurement of proton-capture cross sections on stored, radioactive ions became possible in an energy range of interest for nuclear astrophysics. The experiment was performed at the Experimental Storage Ring (ESR) at GSI by making use of a sensitive method to measure (p,γ) and (p,n) reactions in inverse kinematics. These reaction channels are of high relevance for the nucleosyn-thesis processes in supernovae, which are among the most violent explosions in the universe and are not yet well understood. The cross section of the 118Te(p,γ) reaction has been measured at energies of 6 MeV/u and 7 MeV/u. The heavy ions interacted with a hydrogen gas jet target. The radiative recombination process of the fully stripped 118Te ions and electrons from the hydrogen target was used as a luminosity monitor. An overview of the experimental method and preliminary results from the ongoing analysis will be presented
Horizons: Nuclear Astrophysics in the 2020s and Beyond
Nuclear Astrophysics is a field at the intersection of nuclear physics and astrophysics, which seeks to understand the nuclear engines of astronomical objects and the origin of the chemical elements. This white paper summarizes progress and status of the field, the new open questions that have emerged, and the tremendous scientific opportunities that have opened up with major advances in capabilities across an ever growing number of disciplines and subfields that need to be integrated. We take a holistic view of the field discussing the unique challenges and opportunities in nuclear astrophysics in regards to science, diversity, education, and the interdisciplinarity and breadth of the field. Clearly nuclear astrophysics is a dynamic field with a bright future that is entering a new era of discovery opportunities